git diff from a pre-commit hook

From: Michael Strelnikov <michaelst@gmail.com>
Date: Feb 17, 2020, 09:00 UTC
Message-ID: <CANno94g7S68OfXNJ5B-uKR5=oZn3dsuDsuZHnKrh7tXzYWPNig@mail.gmail.com>

Hello,

   I'm trying to implement the pre-commit hook and faced a problem.
   1. If I just run command "git diff --staged --name-only
--diff-filter=A" I get an error: "fatal: unable to read [SHA]"
   2. After searching for solutions I found that for a pre-commit hook
I have to re-set the GIT_INDEX_FILE variable to ".git/index". After
doing that I see that diff is not honoring the "info/exclude"
settings.

Is there anything else I need to set to make diff working properly?

Best regards, Michael Strelnikov